Military aircraft utilize racks located beneath the wings and fuselage to carry and dispense stores upon command. Stores may be used to contain munitions, i.e. bombs, or to contain other material to be dropped from the aircraft, i.e. rockets or missiles, upon command from the cockpit, for example.
Conventionally, an ejector rack includes a release mechanism which is activated to mechanically release and, subsequently, forcibly eject the stores from the aircraft. Most ejector racks, at one time, utilized pyrotechnic (explosive) cartridges which, upon ignition, generate high pressure gas for actuating the mechanical release mechanism, as well as providing high pressure gas to forcibly eject the stores from the racks mounted on the aircraft.
A characteristic of an ejector rack powered by a pyrotechnic (explosive) cartridge is a short, very high pressure pulse. This high pressure pulse allowed for a reliable removal of the sear from the retaining hook and release of the weapon. The cartridges were somewhat unreliable, however, and their handling, maintenance, and costs were significant.
In order to avoid the problems associated with the pyrotechnic cartridges, the ejector racks migrated to cold gas (pneumatic) systems. As such, an ejection system includes an on-board source of pressurized gas, a release mechanism for mounting the store on the aircraft, and an actuation system for driving the release mechanism between closed and open positions.
The actuation system includes an accumulator for receiving and storing pressurized gas from a source, which may or may not be located on board the aircraft. Actuation of a control valve causes a primary valve to move from a closed position to an open position. This movement allows pressurized gas to flow from the accumulator into the actuation chamber, forcing a separate, hook release piston to move in a linear direction. As a result, the pressurized gas forces a ram attached to the hook release piston to engage and unlock the hooks holding the stores to the rack. Pressurized gas entering the actuator chamber is further capable of exiting from an opposite end of the actuator chamber and flow into one or more feed tubes that deliver the pressurized gas into engagement with thrust pistons. The pressurized gas causes the thrust pistons to forcibly eject the newly unlocked stores from the rack.
While the pneumatic ejection system provides an improvement over earlier pyrotechnic ejection systems, it has been discovered that there was a need to increase the size of the pneumatic ejection system in order to increase the force of the system. In order for the accumulator to accommodate enough pressurized gas to provide sufficient force to unlock the hooks and forcibly eject the stores, the volume of the accumulator needed to be increased. This was achieved by increasing the outer surface area of the accumulator.
Thus, while the pneumatic injection system is able to reduce the overall maintenance costs of the pyrotechnic ejection system, it unsatisfactorily increases the size of the pneumatic ejection system. As a result, the pneumatic ejection system may not fit in a rack that was previously designed to employ a pyrotechnic cartridge, without significant redesign of the rack.
In general, the pneumatic ejection system has a lower peak pressure than the pyrotechnic ejection system. The lower peak pressure of the pneumatic ejection system requires a larger piston area (force=area×pressure) in order to generate the same force, and reliably remove the sear. This is especially more complicated in light of the higher performance of modern aircraft. Packaging of a larger valve hardware, along with its greater weight, is a technical challenge of the pneumatic ejection system.
The heart of the pneumatic ejection system is the accumulator, or the pneumatic power module (PPM). The PPM represents the largest and highest cost component in an ejector rack assembly. The PPM is a combination pressure storage reservoir and two stage valve assembly. The first stage removes the sear from the hook, thereby allowing release of the weapon. The second stage opens the path for the pressurized gas to the ejector pistons, thereby pushing the weapon away. The complication and, therefore cost, is in packaging all the porting required around the large area, and the stroke piston required to reliably remove the sear from the hook under high g-force loads generated by modern fighter aircraft.
Another complication is the sear, which is used to actuate a release of the ejection system. The sear includes a release linkage, which is actuated upon a weapon release command from the cockpit of the aircraft (for example). The sear release linkage needs to be robust (heavy) in order to operate reliably under heavy store loads and high aircraft g-forces.
Another challenge is the requirement for a reversible in-flight lock, or RIFL, as it is commonly known. The RIFL is a safety system that mechanically and electrically “safes” the bomb rack, preventing accidental release, during flight and during ground maintenance operations. The hardware and structural integrity of the RIFL, which is necessary to “block” an accidental firing, is very robust (heavy). This is true even when fabricated from the best (expensive) materials, because of the large forces that must be resisted.
As will be explained, the present invention provides a low force release mechanism for a pneumatic ejection system. The present invention mitigates the complications and drawbacks of conventional pneumatic ejection systems. It also frees up packaging space, thereby allowing easier placement of additional bomb rack sub-systems into the rack.